The invention relates to a self-energizing disc brake and a brake pad therefore.
Self-energizing disc brakes, as are disclosed, for example, in DE 10 2006 036 278 B3, use the tangential forces acting on the brake pad during braking for assisting the brake application force, which is applied by an electromechanical drive or a pneumatically actuated brake cylinder via a brake application device. As a result, the drive may be dimensioned to be considerably smaller.
This self-energizing action is achieved by a self-energizing device which is a component of the brake application device.
In this case, pressure rams which are movable in the axial direction relative to the brake disc are fastened in a guide plate. The pressure rams in each case form a split bearing in cooperation with the brake pad on the brake application side, generally a brake pad having a pad carrier plate which carries a friction pad or a pad pressure plate as a component of the brake pad. Each pressure ram on the front face includes a bearing ball, which is located in a recess provided with ramps sloping upwardly from the inside to the outside in the peripheral direction of the brake disc.
During braking, i.e. when the brake pad is pressed against the brake disc by means of the brake application device, the brake pad is moved due to the friction forces which are produced when coming into contact with the brake disc in the rotational direction thereof, at the same time the associated ramp being moved along the bearing ball, reinforcing the axially aligned braking force which acts on the brake disc.
When releasing the brake, the brake pad is brought into an initial position in which the split bearing is practically ineffective by way of a restoring spring.
During operation, however, problems are produced as the split bearing is substantially unprotected and subjected to the effects of the weather and the environment. This so-called open operation of the split bearing leads to considerable soiling and the appearance of corrosion which may result in the complete failure of the self-energizing device, or at least a reduction in the functionality thereof.
The object of the invention is to develop a self-energizing disc brake and/or a brake pad so that its functional reliability is permanently improved and its service life increased.
This and other objects are achieved by a self-energizing disc brake, comprising a caliper held on a fixed brake carrier, a brake pad on the brake application side and a brake pad on the reaction side, which brake pads may be pressed against a brake disc. A brake application device comprises a self-energizing device as well as a brake ram which may be actuated via a rotary lever and attached to a pad pressure plate, as well as an adjusting device for carrying out adjustments as a result of brake pad wear and/or brake disc wear. The self-energizing device includes at least one pressure ram which bears on its front face against the brake pad on the brake application side via a split bearing and which is secured by its end region facing the brake pad in a guide plate movably held in the brake carrier. The split bearing is enclosed by a sealing arrangement in the non-functioning position of the self-energizing device.
By the enclosure of the split bearing in the unactuated position of the brake, i.e. if, for example, the bearing ball lies in the deepest end position in the recess of the pad pressure plate, the split bearing is protected from the effects of the weather and the operation of the vehicle to such an extent that no moisture or dirt is able to penetrate.
In this case, the surfaces of the pressure ram facing one another and the pad pressure plate bear sealingly against one another in the common coverage region, by the restoring spring, with which the brake pad is pulled out of its braking position, pressing the pad pressure plate and/or the brake pad against the pressure ram. In this case, the front face of the pressure ram and the bearing surface of the pad pressure plate form the sealing arrangement.
For compensating tolerances, preferably on the pressure ram a sealing ring may be provided which, in the initial position of the self-energizing device, bears sealingly against the pad pressure plate and/or the brake pad.
In order to satisfy the mechanical and, in particular, the thermal requirements, the sealing ring is produced from a temperature-resistant, but plasticizable material. To this end, the sealing ring may consist of copper or a temperature-resistant plastics material.
For further corrosion protection, according to an aspect of the invention, the rolling bodies of the split bearing, i.e. generally the bearing balls, are produced from a rust-free and wear-resistant material. To this end, for example, hardenable Cr-alloyed and Ni-alloyed steels, hard metals or ceramics are suitable.
Plain bearing shells, in which the rolling bodies are mounted, may be made from non-rusting or galvanized sheet steel.
The present invention further provides a brake pad for a disc brake, in particular a brake pad for a self-energizing disc brake, comprising a pad pressure plate which carries a friction pad and which has one or both of the following features a) and b): a) at least one recess with a ramp contour formed on the pad pressure plate or on a further plate which may be attached to the pad pressure plate on the side remote from the friction pad, b) the pad pressure plate or the further plate has on the side remote from the friction pad a projection with a receptacle in which a brake ram may be held.
In this manner, further functions are directly incorporated in the brake pad and namely, on the one hand, the at least one ramp contour for the rolling body and alternatively—or particularly preferably additionally—the retention of at least one brake ram. Preferably, the projection is a projection for the middle ram of a total of three brake rams.
According to an advantageous development of the brake pad according to the invention, the ramps of the split bearing are incorporated into a separate insert, which is connected to the pad pressure plate and/or the pad carrier plate, for example by welding.
Alternatively, the ramps may be designed integrally with the pad pressure plate, and may be provided to be sufficiently wear-resistant and corrosion-resistant by appropriate post-treatment. This is integral design may be implemented in a particularly cost-effective and space-saving manner. Moreover, this embodiment provides a guarantee that the corresponding components of the split bearing are not able to be reused when replacing the brake pad.
A trough-shaped design of the guide plate forms a protection of the split bearing from the effects of the weather, primarily from sprayed water acting during the operation of the vehicle, the brake pad and/or the pad pressure plate, in terms of their depth, being partially located in this trough.
The trough edge protrudes, therefore, laterally over the brake pad, whereby in cooperation with a cup-like design of the guide plate in the region of the receiver of the pressure ram, a labyrinth-type seal is formed, which is also effective during braking, i.e. when the brake pad is spaced apart from the pressure ram and/or the guide plate by means of the split bearing and the seal between the pressure ram and the pad pressure plate as a result of the sealing arrangement is no longer as great. By the trough-shaped design of the guide plate, sprayed water and splashed water may not penetrate directly into the gap formed between the guide plate and the pad pressure plate.
In addition or alternatively, as protection of the split bearing, a corresponding seal may be fastened to the respective bearing ball which is designed so that it outwardly seals, firstly, the recess comprising the ramps and, secondly, the bearing region in the pressure ram, i.e. the aforementioned bearing shell.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.